Providing a high energy fiber laser with a narrow linewidth can be a difficult task. Stimulated Brillouin scattering (SBS) is a phenomenon that can be particularly troublesome in relation to achieving such a laser. SBS occurs when light in a medium encounters optical density variations that may alter its energy and path. The optical density variations may be time dependent variations that are caused by acoustic modes, magnetic modes, or temperature gradients. SBS that occurs, for example within high power amplification stages, may create attenuation, power saturation and/or backward propagation of light in a fiber amplifier.
Some techniques have been employed to attempt to reduce SBS for high energy laser applications. For example, techniques including varying the refractive index as a function of fiber radius or modulating the phase of the pump light with an RF noise source of several GHz have both been employed to reduce the optical overlap with the SBS gain spectrum. Other techniques include coiling the fiber or stressing the fiber in some way. However, some of these techniques may not be desirable or optimal in some cases.